The Controversy of Pepsinogen A/Pepsin A in Detecting Extra-Gastroesophageal Reflux

Background: Pepsinogen A (PGA)/pepsin A is often used as a diagnostic marker of extra-gastroesophageal reflux. We aimed to explore whether its positivity in upper aerodigestive tract (UADT) was specific enough to diagnose reflux.

Methods: PGA/pepsin A protein levels were examined in 10 types of tissues and 10 types of body fluid by immunological staining, western blot or Elisa, using three different commercially available brands simultaneously. Liquid chromatography-tandem mass spectrometry parallel reaction monitoring (LC-MS/MS PRM) served as a gold reference for the detection of PGA/pepsin A proteins. PGA gene expression was analyzed by reverse transcriptase sequencing methods for tissue samples. Specifically, 24 hour pH monitoring technique was conducted for patients who donated saliva samples.

Results: Eight out of ten types of human tissue samples (stomach, esophagus, lung, kidney, colon, parotid gland, nasal turbinate and nasal polyps) were confirmed positive for PGA/pepsin A gene and protein by genetic and PRM technique, respectively. Two out of ten types of body fluid samples (gastric fluid, urine) were confirmed positive for PGA/pepsin A protein by PRM technique. The consistence rates of PGA/pepsin A positivity among three commercial antibody brands and Elisa kit were poor, and Elisa results of salivary did not match with 24-hour pH monitoring.

Conclusions: Multiple tissues and body fluid could be detected baseline expression levels of PGA/pepsin A gene and protein. However, those commercially available PGA/pepsin A antibodies achieved poor sensitivity and specificity, therefore, relying on the detection of PGA/pepsin A in UADT by single antibodies to diagnose extra-gastroesophageal reflux without a specific positive cut-off value is unreliable.